Ultrasound transducer assemblies emit ultrasound pulses and receive echoes. In general an ultrasound assembly emits pulses through a plurality of paths and uses the received echoes from the plurality of paths to generate a cross-sectional or volumetric image. Such operation is typically termed xe2x80x9cscanningxe2x80x9d, xe2x80x9csweepingxe2x80x9d, or xe2x80x9csteeringxe2x80x9d a beam. In most ultrasound systems, scanning is rapidly repeated so that many images (xe2x80x9cframesxe2x80x9d) are acquired within a second of time.
Real-time sonography refers to the presentation of ultrasound images in a rapid sequential format as the scanning is being performed. Scanning is either performed mechanically (by physically oscillating one or more transducer elements) or electronically. By far, the most common type of scanning in modern ultrasound systems is electronic wherein a group of transducer elements (termed an xe2x80x9carrayxe2x80x9d) are arranged in a line and excited by a set of electrical pulses, one pulse per element, timed to construct a sweeping action.
In a linear sequenced array, an aperture is swept across the array by exciting sequential (and overlapping) sub-groups of transducer elements. In a linear phased array, all (or almost all) the elements are excited by a single pulse, but with small (typically less than 1 microsecond) time difference (xe2x80x9cphasingxe2x80x9d) between adjacent elements, so that the resulting sound pulses pile up along a specific direction (termed xe2x80x9csteeringxe2x80x9d). In addition to steering the beam, the phased array can focus the beam, along the depth direction, by putting curvature in the phase delay pattern. More curvature places the focus closer to the transducer array, while less curvature moves the focus deeper. Delay can also be used with a linear sequenced array to provide focusing.
When an array is receiving echoes, the electric outputs of the elements can be delayed so that the array is sensitive in a particular direction, with a listening focus at a particular depth. This reception focus depth may be increased continually as the transmitted pulses travel through the tissue of the subject being imaged, focusing along the entire depth of the beam. This continual changing reception focus is called dynamic focusing. The combination of transmission focus and dynamic reception focusing greatly improves detail resolution over large depth ranges in images.
The apparatus that creates the various delays is called a beamformer. Known beamformers have traditionally operated in the analog domain employing expensive beamforming circuits capable of delivering a new point of data (dynamically delayed) every nano-second. More recently, digital beamformers, that provide delay by varying read times out of a digital memory, have been developed. While digital beamformers require extensive memory, exact clock devices and large timing tables, these components are cheaper and smaller than their analog counterparts. Such digital beamformers hold out the hope of cost effective portable ultrasound devices nearly as powerful as their stationary brethren.
Known portable ultrasound devices use a 1-D transducer assembly (known available devices use linear sequenced arrays) in the probe to produce an image taken on a plane that extends from the face of the probe. Currently, there are two classes of portable ultrasound devices: ultrasound specific devices and PC add-on devices.
Ultrasound specific devices are simply miniaturized ultrasound devices, typically with digital beamformers, that replicate larger stand alone units. One example of such a device is the SONOSITE device marketed by SONOSITE, INC. Unlike laptop computers, much of the circuitry and software in large top-of-the-line ultrasound systems is not suitable for miniaturization. Larger traditional components, such as beamformers, lose functionality when miniaturized. PC add-on devices attempt to integrate a transducer assembly and a beamformer in a probe housing. The probe is then connected to a PC, typically a well equipped laptop, to perform image creation from the beamformed data. One example of such a device is the TERASON 2000 by TERASON.
Another area of ultrasound technology receiving significant attention are probes having a transducer assembly comprising a matrix of elements (for example a 56xc3x9756 array of 3,136 elements), sometimes referred to a 2-D or matrix probe. Because matrix probes allow beam steering in 2 dimensions as well as the aforementioned focus in the depth direction, current efforts are related to using matrix transducer assemblies for the capture of a volume of ultrasound data to be used to render 3-D images. Unfortunately, the commercialization of large real-time full bandwidth 3-D images is probably a couple of years off due to lack of affordable image processing resources capable of acting on the volume of data produced by matrix transducers in real-time. To date no known available portable ultrasound devices utilize a matric transducer assembly, probably due to the expense involved with the implementation of a traditional dynamic focusing beamformers multiplied by the number of elements in a matrix probe that must be sampled.
Ultrasound imaging has always involved a tradeoff between image quality and the image processing resources required to process the data from the transducer to obtain the results desired by the user. While the rate at which data can be acquired is limited by physics (sound only travels so fast in the human body), the types of image processing that can be performed on the data is limited by the amount and quality of image processing resources that can be brought to bear upon the data. If real time imaging is desired, as it usually is, another limiting factor is the rate of data acquisition of the processing system.
Ultrasound data is typically acquired in frames, each frame representing a sweep of ultrasound beams emanating from the face of a transducer. 1-D transducers produce a 2-D rectangular or pie-shaped sweep. 2-D transducers are capable of producing sweeps forming a pre-defined 3-D shape, or volume. It is estimated that to fully process a relatively large volume (60xc2x0xc3x9760xc2x0) of ultrasound data in real time, a beamformer capable with 16xc3x97parallelism is required. Such a beamformer would be prohibitively expensive, especially in a market where the acceptable cost of ultrasound systems is rapidly decreasing. Current efforts are focused on ways to short cut full processing while bringing to market a 3-D ultrasound system capable of producing acceptable images at a price point competitive with current 2-D systems. No known portable 3-D solutions are currently available.
FIG. 1 is a block diagram of a known 3-D ultrasound imaging system 100 described in co-pending U.S. patent application Ser. No. 09/633,480 assigned to the assignee of the present application. The apparatus described in the Ser. No. 09/633,480 application uses interleaving to render a 3-D image with the appearance of a real-time image from data produced by a matrix transducer assembly. This allows the use of relatively standard components to minimize cost while providing a state of the art display. The system shown in FIG. 1 is, at the present time, is not available in a portable package.
The ultrasound system 100 utilizes a standard personal computer (xe2x80x9cPCxe2x80x9d) 102, to act as a 3-D image processor and preferably produces an image using interpolated data. The ultrasound system 100 has a matrix transducer assembly 104 and utilizes the concept of sub-group beamforming. In the Example shown in FIG. 1, only elements 106a through 106f are illustrated, but those of ordinary skill in the art will recognize that any number of elements can be utilized. The transducer 104 is preferably configured for sub-group beamforming using a series of ASICs 108n. The use of sub-groups in beamforming is described in U.S. Pat. Nos. 5,997,479 and 6,126,602, both assigned to the assignee of the present application, the subject matter of each being incorporated herein by reference.
Two ASICs 108a and 108b are illustrated, corresponding to elements 106a-f. In the example shown each ASIC 108n is connected to three (3) elements although other designs are possible, for example, 5, 15, or 25 elements could be connected to each ASIC 108n. Each ASIC 108n is provided with a plurality of delay circuits 110n (one for each element connected to the ASIC 108n) that delay the output of a connected element 106n by a programable amount in a known manner so as to focus and steer acoustic beams. A sum circuit 112n combines the output of the delay circuits 110n in each ASIC 108n. 
The output of each ASIC 108n is provided to a scanner 114, preferably located in a main housing of the ultrasound system 100, to complete beamforming. The output of each sum circuit 112n from each ASIC 108n is first A/D converted by a corresponding A/D converter 116n. The converted output of each sum circuit 112n is then delayed by a corresponding delay circuit 118n and subsequently summed with other delayed converted outputs by a sum circuit 120. Circuitry to perform image detection (not shown) is provided, perhaps as part of the sum circuit 120 to produce echo data by performing an image detecting procedure on the summed signal. A scanner control circuit 124 controls the timing and operation of the scanner 114 and transducer 104 using delay coefficients stored in a memory 122. In the case of the system shown in FIG. 1, the delay in each of the delay circuits 110n is kept static throughout reception of a single beam, but the delay in the delay circuits 118n are dynamically varied during reception to achieve dynamic focusing.
The output of the scanner 114 is sent to a back-end 126, provided in the main housing, via an I/O 128 for subsequent signal processing. The back-end 126 performs 2-D signal processing, while the PC 102 performs 3-D image processing. The back-end 126 is provided with a scan converter 130 which converts the 2-D scan data into X-Y space. Subsequent to scan conversion, an image processing unit 131 is provided that can be configured to perform a variety of 2-D image enhancement processes, such as color flow, Doppler, ect . . . , to create image data for display on a monitor 140.
A channel link transmitter 132 transfers the echo data received by the back-end 126 to the PC 102 which receives the echo data via a channel link receiver 134. The channel link can be formed using chip pairs, available from a variety of manufacturers, that conform to the Low Voltage Differential Signaling standard. As shown, the data transferred to the PC 102 is obtained from a data bus in the back end 126 prior to scan-conversion.
A CPU 136 performs computational tasks, including 3-D scan conversion (into X-Y-Z space) under the control of programs stored in memory 138. The CPU 136 creates display data which forms the basis for subsequent output to a monitor 140 (via, for example, an AGP video card (not shown)). The PC 102 performs 3-D rendering and 3-D data manipulation, with the assistance of an expansion card, such as the VOLUMEPRO series of cards supplied by MITSUBISHI. 3-D rendering, as is known to those of ordinary skill in the art, turns 3-D data into data suitable for display on a 2-D screen. The first step in the rendering process is to identify a plane to be imaged along with a point of view. The data set is then sliced and rendered from the selected point of view. Sometimes, the plane is volume rendered, that is enhanced with data from parallel planes xe2x80x9cbehindxe2x80x9d the selected plane. Overall, the differences between images produced by a 3-D system (termed hereinafter xe2x80x9c3-D imagesxe2x80x9d) and those produced by a conventional 2-D system are: a) a 3-D image may have an arbitrary orientation with respect to the face of the probe; and b) a 3-D image can be volume rendered to include image data from nearby slices giving the illusion of depth.
The apparatus illustrated in FIG. 1 is fairly representative of current 3-D ultrasound systems in that a significant amount of processing resources and complex signal processing devices are required to produce a rendered image. In the end though, what is often produced is still essentially a two dimensional image. One of the main concerns for designers of 3-D ultrasound systems is how to produce an image for display from the volume of data. As above, most methods revolve around identifying a plane of interest and displaying data from that plane and possibly sightly behind the plane.
The present inventors have recognized that, in effect, one of the significant contributions of a matrix probe is the ability to image an arbitrary plane within a volume of data. From this, they have discovered apparatus and methods for using a matrix probe to directly image an arbitrary geometry within the field of view of the probe. This allows the presentation of a 2-D image substantially similar to one produced by a conventional 3-D ultrasound system without the need for a significant amount of processing resources or complex signal processing devices. The present inventors have further discovered apparatus and methods for creating a portable ultrasound device that utilizes a matrix probe.